This invention pertains to the art of applying a coating such as paint or the like to an object by dipping the object in an immersion tank.
This invention arose in connection with attempting to develop a method of properly protecting a large integral part assembly, such as the main frame of a transport refrigeration unit, that has previously had only marginal corrosion resistance and thus a potential for premature component failure due to internal corrosion. The part assembly which will be used as an example in explaining the invention is a relatively heavy, transport refrigeration unit frame, which consists of mild steel structural tubing weldment that for cosmetic and cost reasons is mild steel material. The assembly should be properly protected inside and out with a process that is of reasonable cost.
The past method of applying a paint film to the frames constructed by applicant's assignee was by spray painting. Known methods of spray painting result in only marginally complete paint film coverage to a frame that has a complex internal configuration with hollow cavity sections and/or corner spaces which should be protected due to the frame structural design and the potential for corrosion if surfaces are not properly protected. Spray painting, whether conventional, airless, airless electrostatic, electrostatic or powder, all have the same problem; particularly, that spray painting of complex internal surfaces is very time consuming if properly done, thereby resulting in high labor content. Depending upon the product volume, high labor content not only has a great effect on the cost of the product, but an impact on production capacity as well.
Therefore, the aim of this invention is to provide a method of and apparatus for dip coating or painting a transport refrigeration frame in a way that the coating substantially completely covers all surfaces of the frame, and voids from air entrapment in corner spaces and hollow sections is eliminated.